1. Field of the Invention
The present invention relates to an apparatus for observing blood flow patterns by way of ultrasonic beams, where the ultrasonic beams are transmitted to an object such as a biomedical body, and then ultrasonic echoes reflected from the object are processed by phase detectors, whereby the blood flow patterns, e.g., the blood flow patterns in a heart, can be visualized without giving invasive effects to the object.
2. Description of the Prior Art
Due to the development of a real-time ultrasonic tomographic apparatus, a tomographic image of a heart can now be observed. However, an intensity of ultrasonic echoes from a blood flow in the heart is lower than an intensity of ultrasonic echoes from a cardiac muscle by 40 dB or more. For this reason, the blood flow is normally displayed as an echo free component of the ultrasonic echoes in a cardiac tomograph. Therefore, the presence of a blood flow can be estimated, but the flow conditions, i.e., a flow direction, cannot be recognized.
It is known that invisible small bubbles (micro bubbles) are present in pysiological saline and strongly reflect ultrasonic beams. Utilizing this property of physiological saline, physiological saline is injected into a vein of an object to be examined and is circulated together with a blood flow in the heart, thereby displaying a blood flow in a tomographic image. This method is called "a contrast echo method" and is used in practice.
However, the contrast echo method involves an intravenous injection in the object (an invasive method). According to this method, only a blood flow image of the right atrium and ventricle (which pump out a blood flow to the lungs) is displayed. The blood flow of the left atrium and ventricle cannot be displayed although this flow must be clarified as a first priority for diagnostic purposes, resulting in inconvenience.
Another conventional method has been proposed where a blood flow is displayed two-dimensionally by utilizing a Doppler effect.
However, this method does not display the blood flow itself but displays the distribution map of blood flow, which does not give direct information about the direction of the blood flow. In other words, a flow speed is calculated and is displayed. Only the blood flow component (coming toward or going away from the emitting direction of the ultrasonic beam) parallel to the emission direction thereof is given. For this reason, even if the blood flow is oblique along the direction of the ultrasonic beam, information about an actual direction of the blood flow cannot be obtained.
The present invention has been made in consideration of those conventional inherent problems, and has as its object to provide an apparatus for observing blood flow patterns, wherein a blood current direction can be displayed by detecting blood flows parallel to an ultrasonic beam and perpendicular thereto in a noninvasive manner.